People call it the "iPhone 5S" based on Apple's pattern of only
updating internal iPhone specs every other generation. (First
came the iPhone 3G, then the 3GS, then the iPhone
4, then the iPhone 4S, and so on.)

The key differences between the two cases are in the screw
placement and in the text on the reverse side of the phone.

We totally fail to see how slightly different screw placement
merits calling this a brand new phone. This could be an early
prototype of the iPhone
5. It could also be nothing at all.

But hey!

Check out the picture below, which compares the iPhone 5 to the
"iPhone 5S."